Medical devices, such as cardiac pacemakers and ICDs, provide therapeutic electrical stimulation to a heart of a patient via electrodes carried by one or more medical electrical leads and/or electrodes on a housing of the medical device. The electrical stimulation may include signals such as pulses or shocks for pacing, cardioversion or defibrillation. In some cases, a medical device may sense intrinsic depolarizations of the heart and control delivery of stimulation signals to the heart based on sensed cardiac electrical signals attendant to the depolarization of the myocardial tissue. Upon detection of an abnormal rhythm, such as bradycardia, tachycardia or fibrillation, an appropriate electrical stimulation signal or signals may be delivered to restore or maintain a more normal rhythm of the heart. For example, an ICD may deliver pacing pulses to the heart of the patient upon detecting bradycardia or tachycardia or deliver cardioversion or defibrillation shocks to the heart upon detecting tachycardia or fibrillation.
In some cases, ventricular tachyarrhythmia is intentionally induced in a patient by delivering electrical stimulation to the patient's heart in a manner that is arrhythmogenic. Ventricular tachyarrhythmia may be induced in order to analyze the performance of an ICD in detecting the ventricular tachyarrhythmia and terminating it. A patient receiving an ICD to treat atrial or ventricular fibrillation or tachycardia may undergo defibrillation threshold testing in order to ensure reasonable certainty of successful defibrillation using shock pulse energies within the output capacity of the ICD. Some ICDs determine the defibrillation threshold by inducing fibrillation and subsequently delivering one or more defibrillation shocks to verify successful defibrillation at a delivered shock energy that is at least a safety margin below the maximum output of the ICD.